Secondary battery and electrode member thereof capable of being decreased bending deformation after rolling

ABSTRACT

The present application relates to a secondary battery and an electrode member thereof. The electrode member includes an insulating substrate, a conducting layer and an active material layer. The conducting layer is provided on a surface of the insulating substrate, and the conducting layer includes a main portion and a protruding portion extending from the main portion, the main portion is coated with the active material layer, the protruding portion is not coated with the active material layer. The active material layer includes a first portion and a second portion, the first portion is positioned at an end of the active material layer away from the protruding portion, the second portion is positioned at a side of the first portion close to the protruding portion, and a thickness of the first portion is less than a thickness of the second portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT/CN2018/117479,filed on Nov. 26, 2018, which claims priority to Chinese PatentApplication No. 201811206647.4, filed with the National IntellectualProperty Administration of the People's Republic of China on Oct. 17,2018, all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present disclosure relates to the field of battery, and particularlyrelates to a secondary battery and an electrode member thereof.

BACKGROUND

An electrode member of a secondary battery generally includes a currentcollector and an active material layer coated on a surface of thecurrent collector. In order to improve the safety performance of thesecondary battery, some electrode members select a current collectorhaving a multi-layer structure, referring to FIG. 1 and FIG. 2, thecurrent collector includes an insulating substrate 11 and a conductinglayer 12 provided on a surface of the insulating substrate 11, and anactive material layer 13 is coated on a surface of the conducting layer12. The conducting layer 12 includes a main portion 121 coated with theactive material layer 13 and a protruding portion 122 which is notcoated with the active material layer 13. The active material layer 13,the main portion 121 and a portion of the insulating substrate 11corresponding to the main portion 121 form an electric generation regionP1, the protruding portion 122 and a portion of the insulating substrate11 corresponding to the protruding portion 122 form an electric guidingportion P2, the electric guiding portion P2 is used to electricallyconnect with an electrode terminal of the secondary battery and realizecharge and discharge through the electrode terminal.

In the production process of the electrode member, the active materiallayer 13 needs to be rolled thinly, so as to increase energy density.The insulating substrate 11 is made from a softer material (such as PETplastic) with a large extension ratio. Referring to FIG. 2, a thicknessof the electric generation region P1 is much larger than a thickness ofthe electric guiding portion P2, and a roller 9 applies a pressure onlyon the active material layer 13, so the insulating substrate 11 of theelectric generation region P1 has a large extension; during theextension process, the insulating substrate 11 of the electricgeneration region P1 will apply a tension to the insulating substrate 11of the electric guiding portion P2, so as to bring the insulatingsubstrate 11 of the electric guiding portion P2 to extend.Correspondingly, the insulating substrate 11 of the electric guidingportion P2 will apply a reaction force to the insulating substrate 11 ofthe electric generation region P1, so as to limit the extension of theinsulating substrate 11 of the electric generation region P1; in thecase that the thickness of the electric generation region P1 is uniform,the reaction force gradually decreases along a direction away from theelectric guiding portion P2, that is, the extension ratio of theinsulating substrate 11 of the electric generation region P1 graduallyincreases along a direction away from the electric guiding portion P2.Therefore, referring to FIG. 3, after the electrode member is rolled, alength of an end of the electric generation region P1 away from theelectric guiding portion P2 is greater than a length of the electricguiding portion P2, which results in the overall bending of theelectrode member.

In the secondary battery, an positive electrode member and an negativeelectrode member are wound together; if the electric generation regionP1 of the electrode member bends, the end of the electric generationregion P1 cannot be aligned after winding, which causes the activematerial layer 13 of the negative electrode member not to completelycover the active material layer 13 of the positive electrode member; thelithium-ion deintercalated from the active material layer 13 of thepositive electrode member cannot be completely intercalated into theactive material layer 13 of the negative electrode member in chargingprocess, which causes the lithium precipitation and affects theperformance of the secondary battery.

SUMMARY

An electrode member in accordance with some embodiments comprises aninsulating substrate, a conducting layer and an active material layer.The conducting layer is provided on a surface of the insulatingsubstrate, and the conducting layer comprises a main portion and aprotruding portion extending from the main portion, the main portion iscoated with the active material layer, the protruding portion is notcoated with the active material layer. The active material layercomprises a first portion and a second portion, the first portion ispositioned at an end of the active material layer away from theprotruding portion, the second portion is positioned at a side of thefirst portion close to the protruding portion and connected with thefirst portion, and a thickness of the first portion is less than athickness of the second portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an electrode member in prior art.

FIG. 2 is a schematic view of the electrode member of FIG. 1 in arolling process.

FIG. 3 is a schematic view of the electrode member of FIG. 1 afterrolling.

FIG. 4 is a schematic view of a secondary battery according to thepresent disclosure.

FIG. 5 is a cross-sectional view of an electrode assembly according tothe present disclosure.

FIG. 6 is a schematic view of an electrode member according to thepresent disclosure after winding.

FIG. 7 is a schematic view of the electrode member of FIG. 6 afterspread.

FIG. 8 is a cross-sectional view taken along a line A-A of FIG. 7.

FIG. 9 is a schematic view of the electrode member of FIG. 7 in aforming process.

FIG. 10 is a cross-sectional view taken along a line B-B of FIG. 9.

FIG. 11 is a schematic view of the electrode member of FIG. 9 afterrolling.

FIG. 12 is a schematic view of another embodiment of the electrodemember according to the present disclosure.

FIG. 13 is a cross-sectional view taken along a line C-C of FIG. 12.

FIG. 14 is a schematic view of still another embodiment of the electrodemember according to the present disclosure.

FIG. 15 is a cross-sectional view taken along a line D-D of FIG. 14.

REFERENCE NUMERALS IN FIGURES ARE REPRESENTED AS FOLLOWS

-   1 electrode member-   11 insulating substrate-   12 conducting layer-   121 main portion-   122 protruding portion-   13 active material layer-   131 first portion-   132 second portion-   133 third portion-   14 protecting layer-   15 conductive structure-   P1 electric generation region-   P2 electric guiding portion-   2 positive electrode member-   3 negative electrode member-   4 separator-   5 case-   6 cap plate-   7 electrode terminal-   8 connecting piece-   9 roller-   X width direction-   Y thickness direction-   Z height direction

DETAILED DESCRIPTION

The technical solutions of embodiments of the present disclosure will bedescribed clearly and completely in combination with the drawings in theembodiments of the present disclosure, it is apparent that the describedembodiments are only a part of the embodiments of the presentdisclosure, and not all of the embodiments. The following description ofat least one exemplary embodiment is in fact merely illustrative and isnever intended to be any limitation of the present disclosure and itsapplication or use. Based on the embodiments in the present disclosure,all other embodiments obtained by those skilled in the art withoutcreative efforts are within the scope of the present disclosure.

In the description of the present disclosure, it should be understoodthat, words such as “first”, “second” and the like which are used todefine the parts, are only intended to distinguish the correspondingparts. Unless otherwise specified, the aforementioned words do not haveparticular meanings, and thus cannot be understood as limitation on theprotection scope of the present disclosure.

A secondary battery in accordance with some embodiments includes anelectrode assembly, referring to FIG. 5, the electrode assembly includesa positive electrode member 2, a negative electrode member 3 and aseparator 4, the separator 4 is provided between the positive electrodemember 2 and the negative electrode member 3. The positive electrodemember 2, the separator 4 and the negative electrode member 3 arestacked and wound into a flat shape. The electrode assembly is the corecomponent of the secondary battery to realize the charge and dischargefunction.

The secondary battery in accordance with some embodiments is apouch-type battery, the electrode assembly formed by winding thepositive electrode member 2, the separator 4 and the negative electrodemember 3 is directly packaged in a pouch. The pouch in accordance withsome embodiments is an aluminum plastic film.

Certainly, the secondary battery in accordance with some embodiments isa can-type battery. Specifically, referring to FIG. 4, the secondarybattery mainly includes the electrode assembly, a case 5, a cap plate 6,an electrode terminal 7 and a connecting piece 8.

The case 5 has a hexahedron shape or other shape. A cavity is formedinside the case 5 to receive the electrode assembly and an electrolyte.The case 5 forms an opening at one end, and the electrode assembly canbe placed into the cavity of the case 5 via the opening. In someembodiments, the case 5 is made of a conductive metal such as aluminum,aluminum alloy and the like, or the case 5 is made of an insulatingmaterial such as plastic and the like.

The cap plate 6 is provided to the case 5 and covers the opening of thecase 5, thereby sealing the electrode assembly in the case 5. Theelectrode terminal 7 is provided to the cap plate 6, and an upper end ofthe electrode terminal 7 protrudes above the cap plate 6, a lower end ofthe electrode terminal 7 passes through the cap plate 6 and extends intothe case 5. The connecting piece 8 is provided in the case 5 and isfixed with the electrode terminal 7. The electrode terminal 7 and theconnecting piece 8 each are provided as two in number, the positiveelectrode member 2 is electrically connected with one electrode terminal7 via one connecting piece 8, and the negative electrode member 3 iselectrically connected with the other electrode terminal 7 via the otherconnecting piece 8.

In the secondary battery, at least one of the positive electrode member2 and the negative electrode member 3 employs an electrode member 1described later.

FIG. 6 to FIG. 11 are schematic views of a first embodiment of anelectrode member 1 of the present disclosure. Referring to FIG. 6 toFIG. 11, the electrode member 1 includes an insulating substrate 11, aconducting layer 12 and an active material layer 13.

In some embodiments, the insulating substrate 11 is made of a PET(polyethylene terephthalate) film or a PP (polypropylene) film. Athickness of the insulating substrate 11 is 1 μm-20 μm.

The conducting layer 12 is provided as two in number and the twoconducting layers 12 are respectively provided on two surfaces of theinsulating substrate 11. Specifically, a material of the conductinglayer 12 is selected from at least one of a metal conductive materialand a carbon-based conductive material; in some embodiments, the metalconductive material is at least one of aluminum, copper, nickel,titanium, silver, nickel-copper alloy, and aluminum-zirconium alloy, thecarbon-based conductive material is at least one of graphite, acetyleneblack, graphene, and carbon nanotubes. In some embodiments, theconducting layer 12 is formed on the surface of the insulating substrate11 by at least one of vapor deposition and electroless plating. Thevapor deposition method is a Physical Vapor Deposition (PVD), such as aThermal Evaporation Deposition.

The active material layer 13 includes an active material, the activematerial can be determined according to polarity of the electrode member1; for example, when the electrode member 1 is positive, the activematerial is lithium manganese oxide or lithium iron phosphate, and whenthe electrode member 1 is negative, the active material is graphite orsilicon. The active material, a binder, a conductive agent and a solventcan be prepared into a slurry, then the slurry is coated on an outersurface of the conducting layer 12 away from the insulating substrate11, the active material layer 13 is formed after drying the slurry. Theactive material layer 13 is provided as two in number and the two activematerial layers 13 are coated on the two conducting layers 12respectively.

The active material layer 13 covers only a partial region of theconducting layer 12. Specifically, referring to FIG. 7 and FIG. 8, theconducting layer 12 includes a main portion 121 and a protruding portion122 extending from the main portion 121, the main portion 121 is coatedwith the active material layer 13, and the protruding portion 122 is notcoated with the active material layer 13.

For convenience of description, the active material layer 13, the mainportion 121 and a portion of the insulating substrate 11 correspondingto the main portion 121 is referred to as an electric generation regionP1, the protruding portion 122 and a portion of the insulating substrate11 corresponding to the protruding portion 122 is referred to as anelectric guiding portion P2. In the use process of the secondarybattery, the active material layer 13 of the electric generation regionP1 electrochemically reacts with the electrolyte or the like to generatea charge process and a discharge process; and the electric guidingportion P2 is connected with the connecting piece 8 to guide an electriccurrent to the outside of the secondary battery.

Referring to FIG. 7, the electric guiding portions P2 is provided asplurality in number, and the plurality of electric guiding portions P2are arranged to space apart from each other in a width direction X. Inthe secondary battery, an electrode assembly is formed by winding theelectrode member 1 in positive polarity and the electrode member 1 innegative polarity; referring to FIG. 6, after the electrode member 1 iswound, the plurality of electric guiding portions P2 are stacked in athickness direction Y and fixed to the connecting piece 8 by welding.

Since the conducting layer 12 is thin, a burr generated by theconducting layer 12 is small in the cutting process and is difficult topierce the separator 4 having more than ten microns, thereby avoidingshort circuit and improving safety performance. Furthermore, when aforeign matter pierces the electrode member 1 of the secondary battery,since a thickness of the conducting layer 12 is small, a burr generatedby the conducting layer 12 at a location pierced by the foreign matteris small and is difficult to pierce the separator 4, thereby avoidingshort circuit and improving safety performance.

The electrode member 1 further includes a protecting layer 14, theprotecting layer 14 is provided at a side of the protruding portion 122away from the insulating substrate 11 and connected with the activematerial layer 13. The protecting layer 14 includes a binder and aninsulating material, the insulating material includes at least one ofaluminum oxide and aluminum oxyhydroxide. The binder, the insulatingmaterial and a solvent are mixed together to prepare a slurry, theslurry is coated on a surface of the protruding portion 122, and theprotecting layer 14 is formed after drying the slurry. A hardness of theprotecting layer 14 is greater than a hardness of the conducting layer12.

The electrode member 1 further includes a plurality of conductivestructures 15, each conductive structure 15 is welded with a region ofthe protruding portion 122 which is not covered by the protecting layer14. Referring to FIG. 6, after the electrode member 1 is wound, theplurality of conductive structures 15 are stacked in the thicknessdirection Y, and the conductive structure 15 is provided between eachtwo adjacent electric guiding portions P2. The plurality of conductivestructures 15 are welded to the connecting piece 8, so as to achievecollection and transmission of the electric current of the twoconducting layers 12. Referring to FIG. 8, a gap is provided between theprotecting layer 14 and the conductive structure 15.

The active material layer 13 includes a first portion 131 and a secondportion 132, the first portion 131 is positioned at an end of the activematerial layer 13 away from the protruding portion 122, the secondportion 132 is positioned at a side of the first portion 131 close tothe protruding portion 122, and a thickness of the first portion 131 isless than a thickness of the second portion 132.

The electrode member 1 of the first embodiment can be formed by thefollowing steps:

(i) forming a conducting layer 12 on the surface of the insulatingsubstrate 11 by vapor deposition or electroless plating to prepare acomposite strip;

(ii) referring to FIG. 9, coating the active material layer 13 and theprotecting layer 14 on the surface of the conducting layer 12 at thesame time, and reducing the thickness of the end of the active materiallayer 13 away from the protecting layer 14 during coating;

(iii) rolling the active material layer 13 to compact the activematerial layer 13 to increase the density;

(iv) after the rolling is completed, welding a metal foil (for example,aluminum foil) on the conducting layer 12, and then cutting the metalfoil, the protecting layer 14, the conducting layer 12 and theinsulating substrate 11 at the same time to obtain the electrode member1 shown in FIG. 7.

FIG. 11 shows a shape of the electrode member 1 after the rollingprocess of the step (iii). Since the thickness of the second portion 132is greater than the thickness of the first portion 131, the secondportion 132 is subjected to a larger rolling pressure during the rollingprocess, and the first portion 131 is subjected to a smaller rollingpressure; that is, a portion of the electric generation region P1corresponding to the second portion 132 has a larger extension ratio,and a portion of the electric generation region P1 corresponding to thefirst portion 131 has a smaller extension ratio. In the rolling process,the electric guiding portion P2 is not subjected to the pressure andhardly extends, therefore, referring to FIG. 11, after rolling, theextension ratio of the electrode member 1 at both ends in a heightdirection Z is smaller, and the extension ratio of a middle portion ofthe electrode member 1 is larger. The present disclosure reduces thelength difference between the two ends of the electrode member 1 in theheight direction Z by reducing the thickness of the first portion 131,thereby decreasing the bending deformation of the electrode member 1,and in turns preventing lithium precipitation in the secondary battery.

Since an elastic modulus of the insulating substrate 11 is smaller, theinsulating substrate 11 of the electric generation region P1 extendstoward an inner side of the protruding portion 122 when the electricgeneration region P1 is rolled, which causes the insulating substrate 11at the inner side of the protruding portion 122 to bulge, and theprotruding portion 122 is easily cracked under the force of theinsulating substrate 11. In the present disclosure, the protecting layer14 has a greater strength, so the protecting layer 14 can provide asupporting force for the protruding portion 122 in the process ofrolling the electrode member 1, thereby limiting the deformation of theprotruding portion 122, and decreasing the probability of generating thecrack in the protruding portion 122, improving the overcurrentcapability of the electrode member 1.

In the working process of the secondary battery, the protrusion 122 mayfall off due to factor such as vibration or the like; in someembodiments, the protecting layer 14 is connected with the activematerial layer 13, so that the protecting layer 14 is fixed to theactive material layer 13, thereby increasing the connecting force of theprotecting layer 14 in the electrode member 1 and improving theanti-vibration capability, avoiding the protecting layer 14 and theprotruding portion 122 falling off together. At the same time, the crackis most prone to be generated at a root portion (that is, at a boundarybetween the protruding portion 122 and the main portion 121) of theprotruding portion 122 close to the active material layer 13, therefore,when the protecting layer 14 is connected with the active material layer13, it can avoid the protruding portion 122 from being cracked, therebyimproving the overcurrent capability of the electrode member 1.

In the height direction Z, a ratio of a dimension of the first portion131 to a total dimension of the active material layer 13 is from 3% to20%. Since the elastic modulus of the insulating substrate 11 issmaller, a part of the insulating substrate 11 corresponding to thesecond portion 132 will apply a force to a part of the insulatingsubstrate 11 corresponding to the first portion 131 in the rollingprocess, to bring the part of the first portion 131 corresponding to theinsulating substrate 11 to extend; and the force is gradually reduced ina direction away from the electric guiding portion P2. If the ratio ofthe dimension of the first portion 131 to the total dimension of theactive material layer 13 is less than 3%, the end of the electricgeneration region P1 away from the electric guiding portion P2 willstill have a larger extension under the action of the force, which willhave a limited effect on reducing the length difference between the twoends of the electrode member 1 in the height direction Z. If the ratioof the dimension of the first portion 131 to the total dimension of theactive material layer 13 is more than 20%, the capacity of the activematerial layer 13 will be lowered, which affects the energy density.

When rolling, the rolling pressure subjected by the second portion 132is greatest, therefore, after the second portion 132 is rolledcompactly, a density of the second portion 132 is greater than a densityof the first portion 131.

A difference between the thickness of the first portion 131 and thethickness of the second portion 132 is 0.5 μm-20 μm. If the thicknessdifference is less than 0.5 μm, the first portion 131 is still subjectedto a larger rolling pressure, the end of the electric generation regionP1 away from the electric guiding portion P2 still has a largerextension, which will have a limited effect on reducing the lengthdifference between the two ends of the electrode members 1 in the heightdirection Z. If the thickness difference is more than 20 μm, thecapacity of the active material layer 13 is lowered, which affects theenergy density.

Generally, the extension ratio of the insulating substrate 11 is greaterthan the extension ratio of the conducting layer 12, so the insulatingsubstrate 11 will apply a force to the conducting layer 12 in therolling process, so as to bring the conducting layer 12 to extend. If adifference between the extension ratio of the insulating substrate 11and the extension ratio of the conducting layer 12 is too large, theconducting layer 12 is easily fractured under the influence of theforce, which affects the overcurrent capability of the conducting layer12. Therefore, in some embodiments, the difference between the extensionratio of the insulating substrate 11 and the extension ratio of theconducting layer 12 is not more than 4% under the same force. Moreover,the extension ratio refers to a percentage of an extended length of amaterial to an original length of the material under a certain pressure.

The greater the extension ratio of the insulating substrate 11 is, thegreater the length difference between the two ends of the electrodemember 1 in the height direction Z is, at the same time, the more easilythe conducting layer 12 is fractured in the rolling process, so in someembodiments, the extension ratio of the insulating substrate 11 is lessthan 10%. Furthermore, the extension ratio of the insulating substrate11 is from 1% to 3%.

The other two embodiments will be described below. In order to simplifythe description, only the differences between the other two embodimentsand the first embodiment will be mainly described below, and parts thatare not described can be understood with reference to the firstembodiment.

FIG. 12 and FIG. 13 are schematic views of a second embodiment of theelectrode member of the present disclosure. Referring to FIG. 12 andFIG. 13, in the second embodiment, the thickness of the first portion131 is gradually decreased in a direction away from the protrudingportion 122. In order to reduce the length difference between the twoends of the electrode member 1 in the height direction Z, it needs toreduce the extension ratio of the end of the electric generation regionP1 away from the electric guiding portion P2; therefore, in the firstportion 131, the further away from the protruding portion 122 is, thesmaller the thickness thereof needs to be, so as to reduce the lengthdifference between the two ends of the electrode member 1 in the heightdirection Z.

Referring to FIG. 8, in the first embodiment, the first portion 131 isuniformly coated, so the first portion 131 and the second portion 132have a larger thickness difference at a boundary therebetween; thestress concentrates at the boundary between the first portion 131 andthe second portion 132 in the rolling process, therefore, the conductinglayer 12 is easily fractured under the stress, thereby affecting theovercurrent capability. In the second embodiment, the first portion 131gradually becomes thinner in a direction away from the protrudingportion 122, which realizes a smooth transition at the boundary betweenthe first portion 131 and the second portion 132, thereby dispersingstress, and reducing stress concentration, avoiding the stressfracturing the conducting layer 12.

FIG. 14 and FIG. 15 are schematic views of a third embodiment of theelectrode member according to the present disclosure. Referring to FIG.14 and FIG. 15, in the third embodiment, the active material layer 13further includes a third portion 133, the third portion 133 ispositioned at a side of the second portion 132 close to the protrudingportion 122, and a thickness of the third portion 133 is less than thethickness of the second portion 132. The third portion 133 is positionedat the end of the active material layer 13 close to the protrudingportion 122.

The main portion 121 is subjected to the rolling pressure and theprotruding portion 122 is not subjected to the rolling pressure in therolling process, therefore, the stress is concentrated at the boundarybetween the main portion 121 and the protruding portion 122. Referringto FIG. 13, in the second embodiment, the protruding portion 122 isdirectly adjacent to the second portion 132, and the second portion 132has a larger thickness, therefore, the stress at the boundary betweenthe main portion 121 and the protruding portion 122 is too large, andthe main portion 121 and the protruding portion 122 are easily separatedand form a crack, which affects the overcurrent capability. In the thirdembodiment, the stress at the boundary between the main portion 121 andthe protruding portion 122 can be reduced by reducing the thickness ofthe third portion 133, thereby reducing the probability of generatingthe crack.

Furthermore, the thickness of the third portion 133 gradually decreasesalong a direction close to the protruding portion 122. The third portion133 gradually becomes thinner along the direction close to theprotruding portion 122, which realizes a smooth transition at theboundary between the second portion 132 and the third portion 133,thereby dispersing stress, and reducing stress concentration, avoidingthe stress fracturing the conducting layer 12.

Since the protruding portion 122 is adjacent to the third portion 133,the protecting layer 14 is connected with the third portion 133.

What is claimed is:
 1. An electrode member of a secondary battery,comprising an insulating substrate, a conducting layer and an activematerial layer; the electrode member having a symmetric structure withthe insulating substrate at a center of the symmetric structure; theconducting layer being provided on a surface of the insulatingsubstrate, and the conducting layer comprising a main portion and aprotruding portion extending from the main portion, the main portionbeing coated with the active material layer, the protruding portionbeing not coated with the active material layer; and the active materiallayer being composed of a first portion and a second portion, each ofthe first portion and the second portion having a constant thickness,the first portion being positioned at an end of the active materiallayer away from the protruding portion, the second portion beingpositioned at a side of the first portion close to the protrudingportion and connected with the first portion, and a thickness of thefirst portion being less than a thickness of the second portion.
 2. Theelectrode member according to claim 1, wherein in a height direction, aratio of a dimension of the first portion to a total dimension of theactive material layer is from 3% to 20%.
 3. The electrode memberaccording to claim 1, wherein a density of the second portion is greaterthan a density of the first portion.
 4. The electrode member accordingto claim 1, wherein a difference between the thickness of the firstportion and the thickness of the second portion is 0.5 μm-20 μm.
 5. Theelectrode member according to claim 1, wherein the electrode memberfurther comprises a protecting layer, the protecting layer is providedat a side of the protruding portion away from the insulating substrateand connected with the second portion.
 6. The electrode member accordingto claim 5, wherein a hardness of the protecting layer is greater than ahardness of the conducting layer.
 7. The electrode member according toclaim 5, wherein the protecting layer comprises a binder and aninsulating material, the insulating material includes at least one ofaluminum oxide and aluminum oxyhydroxide.
 8. The electrode memberaccording to claim 5, wherein the electrode member further comprises aconductive structure, the conductive structure is welded with a regionof the protruding portion which is not covered by the protecting layer.9. The electrode member according to claim 8, wherein a gap is providedbetween the protecting layer and the conductive structure.
 10. Theelectrode member according to claim 1, wherein the electrode memberfurther comprises a conductive structure, the conductive structure iswelded with a region of the protruding portion which is not covered bythe protecting layer.
 11. The electrode member according to claim 1,wherein, when under a rolling pressure, a difference between anextension ratio of the insulating substrate and an extension ratio ofthe conducting layer is not more than 4%, the insulating substrate ismade of a polyethylene terephthalate film or a polypropylene film, and amaterial of the conducting layer is selected from at least one of ametal conductive material and a carbon-based conductive material. 12.The electrode member according to claim 11, wherein the extension ratioof the insulating substrate under the rolling pressure is less than 10%.13. A secondary battery, comprising an electrode assembly, the electrodeassembly comprising an electrode member; the electrode member comprisingan insulating substrate, a conducting layer and an active materiallayer; the electrode member having a symmetric structure with theinsulating substrate at a center of the symmetric structure; theconducting layer being provided on a surface of the insulatingsubstrate, and the conducting layer comprising a main portion and aprotruding portion extending from the main portion, the main portionbeing coated with the active material layer, the protruding portionbeing not coated with the active material layer; and the active materiallayer being composed of a first portion and a second portion, each ofthe first portion and the second portion having a constant thickness,the first portion being positioned at an end of the active materiallayer away from the protruding portion, the second portion beingpositioned at a side of the first portion close to the protrudingportion and connected with the first portion, and a thickness of thefirst portion being less than a thickness of the second portion.
 14. Thesecondary battery according to claim 13, wherein the electrode memberfurther comprises a protecting layer, the protecting layer is providedat a side of the protruding portion away from the insulating substrateand connected with the second portion.
 15. The secondary batteryaccording to claim 14, wherein the electrode member further comprises aconductive structure, the conductive structure is welded with a regionof the protruding portion which is not covered by the protecting layer.